I have had quite a bit of domains, I manage a dozen or so personally and then a good amount for my main company. I have found time and time again that .coms are the only real recognized domain extention. When I get offers on buying domains, it has always been on the .com version. Sure people want to own the rest, but the website is always rooted on the .com.

Personally If i couldn't get the .com Id move along to another idea.
If it was a nonprofit, a .org is accepatable too... but .nets really seem to default to the back-end IT websites, and people that couldn't get the .com

A word or acronym .com is always the best. And if someone else already has it... and is established, your really going to fighting against their traffic.

Personally if I couldn't get the .com id go .co before going .net or .us.
.com
.org (only if non profit or something of similar nature)

.co
.us
.net

And from there on out I wouldn't use any of the newer 300+ extentions.... its just better to find another name or use a buying service to get the one you want.